Prostacyclin Synthase as an Ambivalent Regulator of Inflammatory Reactions

Prostacyclin (PGI2) synthase (PGIS) and microsomal prostaglandin (PG) E synthase-1 (PGES-1) are PG terminal synthases which functionally couple with inducible cyclooxygenase-2 (COX-2) as their upstream enzymes to produce PGI2 and PGE2, respectively. Non-steroidal anti-inflammatory drugs exert their pharmacological effects by the inhibition of COX-2 and thereby suppression of the biosynthesis of these PGs. PGIS is abundantly expressed in vascular endothelial and smooth muscle cells and has been shown to be critical for regulation of platelet aggregation and vascular tone. In addition to its role in vascular regulation, PGIS has been shown to be expressed in inflammatory cells including macrophages, and the proinflammatory roles of PGIS has been demonstrated. On the other hand, several investigators have recently reported that PGIS functions as an anti-inflammatory mediator by macrophage polarization and have indicated that PGIS is an ambivalent regulator of inflammatory reactions. In this review, we summarize the current understanding of proinflammatory and anti-inflammatory functions of PGIS and discuss its potential as a novel anti-inflammatory therapeutic target.